How to explain callbacks in plain english? How are they different from calling one function from another function?

Question

How to explain callbacks in plain English? How are they different from calling one function from another function taking some context from the calling function? How can thei

Answer 1

There's two points to explain, one is how a callback works (passing around a function that can be called without any knowledge of its context), the other what it's used for (handling events asynchronously).

The analogy of waiting for a parcel to arrive that has been used by other answers is a good one to explain both. In a computer program, you would tell the computer to expect a parcel. Ordinarily, it would now sit there and wait (and do nothing else) until the parcel arrives, possibly indefinitely if it never arrives. To humans, this sounds silly, but without further measures, this is totally natural to a computer.

Now the callback would be the bell at your front door. You provide the parcel service with a way to notify you of the parcel's arrival without them having to know where (even if) you are in the house, or how the bell works. (For instance, some "bells" actually dispatch a phone call.) Because you provided a "callback function" that can be "called" at any time, out of context, you can now stop sitting at the front porch and "handle the event" (of parcel arrival) whenever it's time.